As shown in FIG. 10, two works 101, 102 made of aluminum alloy are butted to each other, and a pin 103 that rotates at a high speed and a shoulder 104 are applied on the butted part. Based on generated friction heat and stirring according to rotation, friction stir welding is performed. The pin 103 and the shoulder 104 are made of steel.
Aluminum (Al) and iron (Fe) have strong affinity. When Fe is caused to come into contact with Al at a high temperature and under a high pressure, Fe and Al react with each other, and an intermetallic compound of an Al—Fe—Si system is generated. The intermetallic compound adheres to the pin 103 and the shoulder 104. As measures for preventing this adhesion, a friction stir welding apparatus shown in Patent Document 1 has been proposed.
As shown in FIG. 11, the friction stir welding apparatus according to Patent Document 1, a diamond-like carbon 105 that prevents adhesion of aluminum is formed on the pin 103 and the shoulder 104. The diamond-like carbon 105 prevents aluminum and steel from coming into contact with each other, and thereby, it is possible to prevent an intermetallic compound of an Al—Fe—Si system from being generated.
However, in the friction stir welding, since the diamond-like carbon 105 comes into contact with a work made of aluminum at a high temperature and under a high pressure, the diamond-like carbon 105 is exfoliated from the pin 103 and the shoulder 104 after a relatively short time. In this way, according to a coating technique using the diamond-like carbon 105, the lifetime of a tool is short. In order to reduce the frequency of replacement of a tool, it is required to extend the lifetime of the tool.
In the technique of Patent Document 1, a process head is provided movably in the horizontal direction on a gate-shaped column, and a rotation tool is provided on the process head. Therefore, the size of the friction stir welding apparatus is increased.